If they are both cleared of spirit attachments, can they have a stable love relationship?

We cannot guarantee anything about human behavior, given it is not under our control, but we see these two having a karmic history together in the past that has been quite workable and beneficial. Being together will allow them to continue doing mutual healing for past traumas in other lifetimes and that will contribute to learning and growth for both parties. The key is removing the malevolent influence in their way coming from outside consciousness. Once they are left to their own devices, truly, we see they would be able to keep their relationship going in a productive way. It is up to them and their choice, and that is as it should be, and not under a cloud introduced by a malevolent force.